For the last several decades I have built suction boxes and I have
bought them.  I think there is no reason to build one -- it is an
annoying process.  You have to find just the right motor among the
dozens at Grainger; you must figure a way to soften the noise; you
must select wood, plywood or pressed wood.

You must find a way to mount the motor into the box and also find a way
to add a flap valve so the piano can be pedaled as well.  You must also
design a speed control for the motor and there is not one commercially
available that is acceptable.

Don't bother with any of that!  Just contact Eric Bergstrom and get
his state of the art, super quiet unit, "The Bergytone", that cannot
be improved on.  Also the price is about what it will cost you to build
it and it is _way_ less than it will cost you to design a two-stage
power controller for both play and reroll speeds.  Eric is at

  http://pianoproservice.com/ 
  http://pianoproservice.com/bt-002.html 

Doug L. Bullock
tel.: 1-314-772-6676
http://thepianoworld.com/